You may not be surprised that I disagree with you somewhat.
First, on the 4e MM: it has the following to say about Hook Horrors (I've slighltly toyed with the sequencing, and elided some of the content, including repetition):
Hook horrors drag victims to their deaths using their powerful hooked arms. These pack omnivores scour the Underdark in search of live prey, foraging when necessary. . . Hook horrors are omnivorous but prefer meat to plants. Rumor has it that they prefer the flesh of drow over any other. Not surprisingly, drow slay wild hook horrors and take young and eggs to raise as slaves. . .
Hook horrors live in total darkness. They can see in lit environments, but in the dark of the deep earth they navigate using echolocation. They Hook horrors communicate with one another using . . . clicking noises they make with their mouths and carapace. . . An Underdark explorer might become aware of nearby hook horrors by these noises. . . The eerie clicks echo in the Underdark, warning prey that death is near. . .
Although they hunt in small packs, hook horrors also gather in larger groups called clans. A particular clan, ruled by its strongest egg-laying female, ranges over a wide area in the Underdark. Its members defend clan territory fiercely from any intruder, including unrelated hook horrors.
I think that is quite a bit of "fluff". It doesn't strike me as being all about combat at all. I learn about matriarchal clan structure, a fondness for drow (suggesting to players that hook horrors could be used to advantage in a War of the Spider Queen or Vault of the Drow-type scenario), and the taking of eggs for enslavement. We certainly get told about the preference for meat, and - as far as brining cows is concerned - there is no reason why this couldn't be resolved as a simple skill challenge.
Second, more generally - I don't find the "rules should follow story" mantra very useful. Mechanics, in my view, should
evoke story. If a situation is meant to be scary to the players, or tense, the mechanics should help induce that experience. For me, this is the significance of 4e's tactical mechanics - the players have to think hard, and the game can spend a long time in a difficult and complex situation where the outcome remains in doubt. In my RPGing experience, that's not a bad way to try to evoke an appropriate emotional response in half-a-dozen people sitting around someone's kitchen table.
I'm not surprised that you disagree, but I'm glad you posted. I almost always learn something when you do.
EDIT: AND, welp....I'll be damned! I had written this after a quick glance at the MM to see what you were referring to.
To address your first comment part: That IS quite a bit of story/ecology/fluff. This is one of those cases where the example chosen does not adequately represent the rule. (Course, it was chosen because of the 5e article, not as the posterchild for the 4e MM1).
I still think what I mentioned about the history with 4e MM1 was pretty fair and accurate. Yes, the hook horror has a section of lore...one that's pretty robust actually. But turn to hound or hydra and you'll see what I mean. As a whole, the first MM1 skimps on story/ecology/fluff. Unless I recall incorrectly, and I'm fairly sure I'm not...but I'd be open to being corrected, a number of people didn't like that (and defenders of fluffless monster entries liked it because "they weren't tied to existing fluff", "they could just make their own", and "WotC could pack in more monsters". I also think that WotC heard this message loud and clear, and that they changed modalities for future 4e monster manuals, including more story/ecology/fluff/lore.
But yeah, the hook horror. It has adequate 4e fluff, IMO.
Then I went back, thinking I was right, as the blurb describing the hound and hydra was, as I had been used to, significanty boring and short. But then I read on. It seems that I'm mistaken, and my beef with 4e's MM1 was a matter of formating the information, not an absence of it. Most of the info is built into the lore section (which makes sense as it tells a player how much their character knows...the DM should just read it all). Since I've never DMed 4e, and only read the intro to each monster (not wanting to get into the rules because of player spoilers) I didn't notice/wasn't aware of the fact that most of the info was in lore.
I still do remember a hubbub about the supposed lack of information, though. Maybe many others were mistaken like me? Perhaps the information was there, but wasn't interesting to read in the format they used, making the book more of a reference book (my son likes for me to read my 2e monster manual to him for bedtime stories....I'm positive, even with my newfound respect for 4e MM1, that he wouldn't want me reading from that one). There is still
something about the 4e MM1 that I dislike in terms of monsters as "beings"...but I'm now having a much harder time putting my finger on it. Maybe it goes back to that bedtime story component. I'll have to think more on this.
So, yeah. I guess you were right. Good on ya! Guess I learned something from you (again).
To your second part:
I'm not sure I disagree with you (or that you're disagreeing with my overall point.) Rather, it may be the terminology or us talking past one another (or my being unclear).
Perhaps a better way to say it would be "rules should harmonize with story".
My main point is that in creation of a monster there should be an idea, or theme...a purpose for the monster, a set of goals and motivations. I suppose this is the kernel of the monster that starts before any rules or story.
After that, care should be taken that the rules evoke that idea, and make for a good story. Care should also be taken that the development of the story is supported by rules that make sense for that thematic kernel.
What should NOT happen is a selection of rules to fit that kernel with little attention to the monster as a "being", even if it is a dynamic and interesting combat machine.
It's been hard for me to clearly state exactly what I mean...but basically a harmony or synergy between the monster as a "Real thing" and the monster as a "tool in the game to create excitement, atmosphere, and event".
Maybe an example would be somewhat clearer:
If the creature could be replaced by a mindless automoton or golem (even a scary/cute/humorous one as the situation calls for it), but keep the same rules for the creature, then it has failed as a creature, in my opinion. I can't remember exactly, whether golbins or kobolds can do this, or if I'm totally muddled...but, let's say kobolds get a shift as an immediate action any time they are missed. This is an excellent rule in terms of creating a style of "frustrating little buggers". However, if that's ALL we know about them, not their proclivity with traps, their tendency to serve dragons, that they'll only attack in superior numbers, that they're essentially cowards, but greedy desperate cowards...
Then we essentially could replace them with "frustrating little bugger" robots. It'd still evoke the same feeling from the rule; it'd still do everything the kobolds do (assuming that was all we knew about them from the monster manual...not the other things I mentioned).
Hopefully that makes my point more clear: that there is a need for the ecology in order to consider the monster beyond just the encounter...and even within the encounter itself (if kobolds are cowards who depend on superior numbers, they should flee after half of em are down).